1. Field of the Invention
The present invention relates to a process and system to convert thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and electrical energy.
More particularly, the present invention relates to a process and system to convert thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and electrical energy, where a working fluid comprises a mixture of at least two components, with the preferred working fluid comprising a water-ammonia mixture.
2. Description of the Related Art
Prior art methods and systems for converting heat into useful energy at well documented in the art. In fact, many such methods and systems have been invented and patented by the inventor. These prior art systems include U.S. Pat. Nos. 4,346,561, 4,489,563, 4,548,043, 4,586,340, 4,604,867, 4,674,285, 4,732,005, 4,763,480, 4,899,545, 4,982,568, 5,029,444, 5,095,708, 5,440,882, 5,450,821, 5,572,871, 5,588,298, 5,603,218, 5,649,426, 5,822,990, 5,950,433 and 5,593,918; Foreign References:7-9481 JP and Journal References: NEDO Brochure, xe2x80x9cECO-Energy City Projectxe2x80x9d, 1994 and NEDO Report published 1996, pp. 4-6, 4-7, 4-43, 4-63, 4-53, incorporated by reference.
Although all of these prior art systems and methods relate to the conversion of thermal energy into other more useful forms of energy, all suffer from certain inefficiencies. Thus, there is a need in the art for an improved system and method for converting thermal energy to more useful forms of energy, especially for converting geothermal energy into more useful forms of energy.
The present invention provides a process for converting thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and/or electrical energy, where the process includes the steps of expanding a fully vaporized, high pressure, working fluid stream, transforming its energy into usable form and producing a returning or spent, low pressure, stream. The fully vaporized working stream is produced by evaporating an upcoming liquid working stream using heat derived from a heating stream from an external heat source, a sufficient portion of the spent, low pressure, stream, and a first portion of a vapor sub-stream derived from the sufficient portion of the spent, low pressure, stream after partial condensation in heating the upcoming liquid working stream to form the fully, high pressure, vaporized working stream. An additional amount of usable energy is derived from expanding a second portion of a vapor sub-stream derived from the sufficient portion of the spent, low pressure, stream after partial condensation and a remainder portion of the spend, low pressure, stream, transforming its energy into usable form and producing a secondary returning or spent stream, where an amount of usable energy is increased from about 20% to about 30% over prior art processes.
The present invention provides a system including a multi-component basic working fluid, a geothermal source stream, and a cooling stream. The system further includes equipment necessary to establish a thermodynamic cycle capable of converting from about 20% to about 30% more thermal energy into mechanical energy than the prior art thermodynamic process of U.S. Pat. No. 4,982,568. A preferred system includes six heat exhangers, two pumps, a separator and a throttle valve.
The present invention provides an apparatus including a means for expanding a fully vaporized working stream, transforming its energy into usable form and producing a spent stream; a first heat exchange zone for cooling an external heat source and transferring heat from the external heat source to a heated upcoming liquid working stream to form the fully vaporized working stream; and a second heat exchange zone for partially condensing a sufficient portion of the spent stream to form a partially condensed sufficient portion of the spent stream and for transferring heat from the sufficient portion of the spent stream to a pre-heated upcoming liquid working stream. The apparatus also includes a pre-heater for partially condensing a first portion of a vapor sub-stream separated from the condensed sufficient portion of the spent stream to form a primary spent stream and for transferring heat from the vapor sub-stream to an upcoming liquid working stream and a means for expanding a second portion of the vapor sub-stream and a remaining portion of the spent stream, transforming their energy into usable form and producing a secondary spent stream. The apparatus further includes a means for condensing the primary and secondary spent stream into the upcoming liquid working stream.